Hydrogen fluoride, or hydrofluoric acid (HF) is highly toxic and corrosive. However, it is used as a catalyst in isomerization, condensation, polymerization and hydrolysis reactions.
The petroleum industry uses anhydrous hydrogen fluoride primarily as a liquid catalyst for the alkylation of olefinic hydrocarbons to produce alkylate for increasing the octane number of gasoline. It is estimated that the U.S. petroleum alkylation industry uses 5% of the HF produced in the U.S. Its importance and acceptance is evidenced by the fact that in 1978 U.S. refiners scheduled eight new HF alkylation plants with a total capacity of 7,950 m.sup.3 (50,000 barrels) of alkylate per day. The total U.S. HF alkylation capacity in 1984 was 69,160 m.sup.3 (435,000 barrels) per day, and 0.43 to 1.0 kg of HF were used per cubic meter of alkylate.
Years of experience in its manufacture and use have shown that HF can be handled safely, provided the hazards are recognized and precautions taken. Though many safety precautions are taken to prevent leaks, massive or catastrophic leaks are feared primarily because the anhydrous acid will fume on escape creating a vapor cloud that can be spread for some distance.
A number of qualitative methods have been proposed for treating HF spills. The most common method is the use of a simple water drench system. Kirk-Othmer: Encyclopedia of Chemical Technology 3rd Edition, Volume 1, page 655 reports that "water, the most common absorption liquid is used for removing acidic gases...especially if the last contact is with water of alkaline pH". However, because of the aerosol nature of the HF cloud, i.e., the HF droplets in such a cloud are very small compared to the droplets of water in a simple water drench, the water drench generally cannot remove all the HF present in the cloud.
U.S. Pat. No. 4,210,460 relates to treating an HF liquid spill by applying to the spill a quantity of an aqueous solution of calcium acetate equal to at least seven times the estimated volume of the spill, and thereafter treating the spill with powdered magnesium oxide and a pH indicator such as bromothymol blue. After the mixture reaches a persistent blue color, indicating a safe state, the spill is cleaned up mechanically.
At the 1982 Hazardous Material Spills Conference, Edward C. Norman of National Foam System Inc. reported the application of limestone and then CHF-784 foam (a proprietary composition) to the contents of a damaged tank emitting an HF cloud. An immediate reduction in fume evolution was apparent after the foam application.
Gordon K. Braley, at the proceedings of the 1980 National Conference on Control of Hazardous Material Spills, in Louisville, Ky. on May 15, 1980 reported the treatment of relatively small amounts of controlled liquid spills of anhydrous hydrogen fluoride with high molecular weight polymers including polyacrylamide, polymethyl methacrylate, and polyvinyl alcohol. These materials applied in the form of a bead polymer formed a "skin" over the spill preventing fuming of the liquid. Polyacrylamide was deemed the most effective skin-forming agent.
Of the art cited above, only Edward C. Norman discusses an alleged successful treatment of a cloud containing HF. However, the composition used to treat such a cloud is not disclosed t the public.
The present invention was devised to provide an effective method and apparatus for containing an HF cloud.